1. Field of the Invention
The present invention relates to an ignition device and an ignition method for an internal combustion engine for igniting a combustible mixture in a combustion chamber of the internal combustion engine.
2. Description of the Related Art
In recent years, there have been posed problems such as the environmental conservation and the fuel exhaustion, and a response to those problems is an urgent matter in the automobile industry. As measures to these problems, the ultra-lean combustion (stratified lean combustion) operation of an engine using a stratified mixture, for example, is known. However, a distribution of a combustible mixture may vary in the stratified lean combustion, and an ignition device capable of absorbing this variation is required.
In order to satisfy the above-mentioned requirement, there is proposed an ignition device, which includes an ignition plug for generating a spark discharge in a combustion chamber and a microwave generation device for feeding energy to the spark discharge of the ignition plug (refer to Japanese Patent Application Laid-open No. 2010-96128, for example).
This ignition device can form large discharge plasma, increase spatial ignition opportunities, and absorb the variation in distribution of the combustible mixture. Therefore, the ignition device can satisfy the requirement for the stratified lean combustion.
However, the related art has the following problems.
The ignition device described in Japanese Patent Application Laid-open No. 2010-96128 can form large discharge plasma, and hence can prevent a misfire to restrain a variation in generated torque, but a passage for supplying the microwave into the combustion chamber is required in addition to the ignition plug. Therefore, there is a problem in that it is difficult to apply the ignition device according to Japanese Patent Application Laid-open No. 2010-96128 to an existing engine.
Moreover, in the combustion chamber, a large change in pressure is repeated by a reciprocal motion of a piston, and the formation and an extinction of plasma are repeated by the discharge and combustion, which leads to a very unstable state. Therefore, there is a problem in that a stable supply of high frequency energy such as the microwave to the combustion chamber is very difficult in impedance matching and the like technically and in terms of matching individual products.